I could determine that the shingles are a second layer over the first.

I could tell that the plumbing penetration collar was not replaced.

Often they aren't as the new shingles just go over the old.

Why change anything regarding the lower shingles? The objective is to be quick and get paid.

Plumbing penetration collars don't last forever. It's best to replace them along with a new shingle installation.

They apparently did not here. See the roof leak? See the dimple? See the stain on the back side of the dimple? There was dripping evidence that day!

Dimples really are attractive on little girls. And even on big girls! But not on insulation.

My recommendation: leave the dimples to pretty faces and not to insulation. Replace your plumbing penetration collars, people! Do it now. Resistance is futile. Or face the wrath of the home inspector's camera. I hear they all have them now.

Nothing a tub of tar couldn't fix! Ok, maybe 2 tubs. I have never understood doing a roof over, the poor guys that have to remove 2 layers (someday) to re-roof will be cussin! Not to mention the added weight on the truss structure... sheeesh!